The present invention relates to a semiconductor integrated circuit and its production having a fuse element that is formed as part of the integrated circuit, and, more particularly, to a fuse element formed as part of the integrated circuit that has a low insertion loss.
Fuse elements have been incorporated in semiconductor integrated circuits to enable permanent alteration of a basic circuit design, i.e., to produce the so-called application specific integrated circuits (ASIC""s). When left undisturbed, the fuse elements provide conductor paths between certain circuit devices. The fuses may also serve as resistive elements. The fuses can be blown to destroy selected paths of conductivity whereby a circuit function can be permanently altered, i.e., customized. Typically, the fuse elements are burned off (blown) by impinging a high energy laser beam on the fuse.
A disadvantage with known fuse elements incorporated in an integrated circuit is the high insertion loss caused by the fuse element since its resistance is in series with a high current path. The resistance of such known fuse elements is on the order of 200 to 300 milliohms.
It is desirable to provide a fuse element in an integrated circuit that has a low insertion loss. It is desirable to provide a fuse element in an integrated circuit that has a resistance of one order of magnitude less than known fuse elements.
It is also desirable to provide a fuse element that isolates multiple nodes within the integrated circuit from an external contact pad without disrupting the connectivity of the internal nodes to each other.
In accordance with a first aspect of the invention, there is provided an integrated circuit having a conductive path and a fuse element. The conductive path couples a first point to a second point. The fuse element couples the conductive path to a third point. The fuse element is formed in the conductive path between the first point and the second point. The fuse element is defined by a plurality of openings formed through the conductive path so that when the fuse element blows, the third point is electrically isolated from the conductive path while the first point remains electrically coupled to the second point.
In accordance with a second aspect of the invention, there is provided an integrated circuit for controlling the charging of a battery cell located remotely from the integrated circuit. The integrated circuit includes a first switch, a second switch and a fuse element. The first switch is coupled to a first conductive path and receives first control signals. The second switch is coupled between the first conductive path and a first pin. The fuse is coupled between the first conductive path and a second pin. The second pin can be coupled to a current source that is located remotely from the integrated circuit when the circuit is in use. When the integrated circuit is in use and the battery cell is being charged with current from the current source, the first switch is in an off condition and the second switch is in an on condition to direct current from the current source to the battery cell. When the current exceeds a predetermined level, the fuse blows open thereby isolating the current source from the integrated circuit without interrupting the conductive path.
In accordance with a third aspect of the invention, there is provided an integrated circuit having a fuse element formed therein. The circuit includes a substrate, a layer of metal disposed over the substrate, a plurality of openings formed through the layer of metal that encircle a region of the layer of metal and a contact pad coupled to the region of the layer of metal where the region and contact pad form the fuse element.
In accordance with a fourth aspect of the invention, there is provided a method for making an integrated circuit having a fuse element formed therein. The method includes the steps of disposing a layer of metal on a substrate, forming a plurality of openings through the layer of metal wherein the plurality of openings encircle a region of the layer of metal, and coupling a contact pad to the region of the layer of metal wherein the region of the layer of metal and the contact pad form the fuse element.
A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawings, which are briefly summarized below, to the following detail description of presently preferred embodiments of the invention, and to the appended claims.